Hitherto, as photosensitive resin plates for flexographic printing, plates of photosensitive resin compositions which are developed with organic solvents have been known. However, these printing plates have problems of safety for the human body and environment due to use of organic solvents, for example, toxicity, flammability and the like.
In view of this, recently, it has been proposed to use flexographic printing plates of photosensitive resin composition which can be developed with an aqueous system instead of the above plates.
For example, Japanese Patent Kokai No. 52-134655 discloses a photosensitive resin composition which comprises a copolymer containing as essential components a conjugated diene hydrocarbon and a .alpha..beta.- ethylenic unsaturated carboxylic acid and also containing a monoolefin unsaturated compound, as well as a photopolymerizable unsaturated monomer and a photosensitizer. Japanese Patent Kokai No. 60-211451 discloses a photosensitive elastomer composition which comprises as essential components a conjugated diene hydrocarbon polymer or a copolymer of a conjugated diene hydrocarbon and a monoolefin unsaturated compound, a hydrophilic polymer, a non-gaseous ethylenic unsaturated compound and a photopolymerization initiator.
These compositions can be developed by an aqueous developing solution, for example, an aqueous alkali solution or an aqueous alkali-organic solvent system. However, the compositions have problems that their ozone resistance, weathering resistance and oxidation resistance which are required for a flexographic printing plate are insufficient because their bases are conjugated diene hydrocarbons
Further, the fundamental characteristic property of a photosensitive resin composition is an optical property, namely, light transmission property and, therefore, good compatibility between components is required. In this respect, because many of hydrophilic polymers to be contained in such a composition have originally high polarity, preferably, other components to be mixed also have high polarity. However, generally, polymers of conjugated diene hydrocarbons have low polarity and therefore they have a defect that the kind and the mixing ratio of a hydrophilic polymer having good compatibility are limited.
In Japanese Patent Kokai No. 62-133449, there is disclosed a photosensitive resin composition which can be developed with an aqueous system. This composition comprises (A) a water soluble polymer and its photo-crosslinking agent or a photo-crosslinkable water soluble polymer and (B) a copolymer the main copolymerizable components of which are vinylidene chloride and (meth)acrylic acid and/or a (meth)acrylic acid derivative. However, this composition is used for a screen printing plate and there is no suggestion of a flexographic printing plate.